fix: reject server function calls on 5xx responses without X-Error

.changeset/rotten-spoons-reject.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/start": patch
+---
+
+Reject server function calls when the response is a 5xx without an X-Error header, instead of resolving with the parsed error body

apps/tests/cypress/e2e/server-function.cy.ts

@@ -52,4 +52,14 @@ describe("server-function", () => {
     cy.visit("/generator-server-function");
     cy.get("#server-fn-test").contains('¡Hola, Mundo!');
   });
+  it("should reject the promise when the response is a 5xx without an X-Error header", () => {
+    cy.intercept("POST", "/_server*", {
+      statusCode: 500,
+      headers: { "content-type": "application/json" },
+      body: { statusCode: 500, statusMessage: "boom" }
+    });
+    cy.visit("/server-function-rejected-on-500");
+    cy.get("#call").click();
+    cy.get("#server-fn-test").contains("rejected");
+  });
 });

apps/tests/src/routes/server-function-rejected-on-500.tsx

@@ -0,0 +1,24 @@
+import { createSignal } from "solid-js";
+import { serverFnWithIsServer } from "~/functions/use-is-server";
+
+export default function App() {
+  const [output, setOutput] = createSignal("pending");
+
+  const call = async () => {
+    try {
+      await serverFnWithIsServer();
+      setOutput("resolved");
+    } catch {
+      setOutput("rejected");
+    }
+  };
+
+  return (
+    <main>
+      <button id="call" onClick={() => void call()}>
+        call
+      </button>
+      <span id="server-fn-test">{output()}</span>
+    </main>
+  );
+}

packages/start/src/runtime/server-runtime.ts

@@ -88,8 +88,8 @@ async function fetchServerFunction(
       result = await deserializeJSONStream(cloned);
     }
   }
-  if (response.headers.has("X-Error")) {
-    throw result;
+  if (response.headers.has("X-Error") || response.status >= 500) {
+    throw result ?? new Error(`Server function call failed with status ${response.status}`);
   }
   return result;
 }